1. Field of the Invention
This invention relates to a device for cell culture production, and more particularly to a vessel and closure assembly having means for varying the gas diffusion rate into and out of the vessel.
2. Description of Related Art
Typically, cells are cultured under conditions in which the hydrogen ion concentration (pH, the negative logarithm of the hydrogen ion concentration), temperature, humidity, osmolarity and concentration of certain ions are controlled within relatively narrow limits.
Vessels that are used in such tissue culture systems are typically made from plastic and include closures. Such vessels and closures are illustrated in U.S. Pat. Nos. 4,289,248, 4,387,822, 4,770,308 and 5,047,347.
In typical eukaryotic cell culture systems, pH is maintained near physiologic levels by utilizing a buffering system in the tissue culture fluid, in conjunction with an incubator in which carbon dioxide (CO.sub.2) is infused at a rate sufficient to maintain a concentration in the incubator atmosphere of approximately 5 to 7 volume percent. The CO.sub.2 reacts with water to form a weak acid and a carbonic acid, which in turn interacts with the buffering system to maintain the pH near physiologic levels. Entry of CO.sub.2 from the incubator into the tissue culture vessel is generally achieved by utilizing a closure on the vessel such as, a loosely fitting cap, lid, a stopper or a cap with a mircroporous or gas permeable membrane. Equilibrium in the vessel is maintained by allowing gas exchange with the inside of the vessel and the atmosphere of the incubator while preserving sterility and preventing liquid leakage. Alternatively, a loosely fitting cap, lid or stopper is partially opened to either to an approximate extent determined by the user or by the closure design.
Removal of the vessel from the controlled atmosphere of the incubator is often required during growth and culturing of cells. The vessels are usually removed for inspection and media manipulation, subculturing or treatment of the cells and culture fluids. It is important that the pH of the cell culture be maintained close to the desired physiologic level while the vessel is outside of the incubator.
A special need exists for an improved closure assembly for a culture vessel which (1) provides rapid and uniform equilibration between the vessel atmosphere and the incubator; (2) allows the culture vessel to be removed from the controlled atmosphere of the incubator for reasonably long times without subjecting the cell culture to undesirable changes in the pH of the system; and (3) is reusable.